Heat Balance

Question 1

Heat Balance

When performing a normal ramp what power indication do we normally “drive” by?

Why do we use this value first VS. another parameter?

Answer 1

Order of preference

• U4300 A15 (15 min avg of Core thermal pwr)
• DFWCS (secondary cal)
• U1169 A05 (5 min avg PPC PR NI’s)
• NR 45, NI’s (CC1), NI’s (NI racks)

most acurate representation of power (NI’s are indicating fast neutron leakage => temp, flux, etc deviations will make indication innaccurate

Question 2

Heat Balance

How does the Axial flux change over core life?

How are PR NI’s gains adjusted to compensate for these changes?

Answer 2

Flux

• starts as bell curve low at perifery and high in center
• shifts higher in center and lower at perifery due to IFBA in new fuel (loaded in center) burning out
• after IFBA burnt out/ fuel now burning out faster than IFBA flux starts lowering in center and rising at perifery

Gain

• flux in center rise and lowers at perifery => leakage to NI’s lowers => adjust gain up
• as flux lowers in center and raises at perifery => leakage to NI’s raises => adjust gain down for rest of core life

Question 3

Heat Balance

What does ANHL stand for?

What is the purpose of this term?

Answer 3

ANHL - average net heat loss

Purpose - it takes into account any outside heat transfered (primarily heat added by RCP’s) from primary to secondary that is not done by Rx.

this term is subtracted because the major contributer is heat added by RCP’s => value must be taken away from CTP

Question 4

Heat Balance

What does NFF stand for?

What does this term account for? How/Why would this term change?

Answer 4

Nozzle fouling factor

heat is calculated by mass flow rate via D/P. If the venturi’s that give us D/P fouled they would read a higher value than actual => indicated power would be HIGHER than actual

What could be done is adjusting NFF < 1.0 therefore indicated power would lower to = actual power

if fouling went away, you could exceed power limit